Endothelium. A typical endothelial cell is about 30mm long, Accounts for 1% or less of the arterial weight

Transcription

1 Endothelium Discovered in 1845 A typical endothelial cell is about 30mm long, 10mm wide, and mm thick Accounts for 1% or less of the arterial weight As recently as the late 1960s it was thought of as merely a sheet of cellophane

2 Prostacyclin and NO fundamental mediators in the vasculature

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4 Bioassay profile of different vasoactive substances

5 One great advantage of bioassay is that it measures biological activity

6 Snap Crackle Pop

7 Arachidonic acid Prostaglandin F 2α Prostaglandin E 2 Metabolic pathway of arachidonic acid, 1971

8 This explained the mechanism of action of aspirin-like drugs and at least one of their side effects _ the gastric damage

9 Experiences with aspirin (acetyl salicylic acid) in the nonspecific prophylaxis of coronary thrombosis Craven (1953) Mississippi Valley Med. J. 75: 38-44

10 Arachidonic acid cyclic endoperoxides PGG 2, PGH 2 thromboxane A 2 prostaglandin F 2α prostaglandin D 2 C17 hydroxyacid malondialdehyde MDA prostaglandin E 2 Metabolic pathway of arachidonic acid, 1975

11 Platelet aggregation induced by PGG 2 and TXA 2 PGG 2 500ng PGG 2 250ng PGG 2 100ng TXA 2 extracted From 100ng PGG 2 Optical density 2 min Needleman et al, (1976) Nature 261:

12 Arachidonic acid cyclic endoperoxides PGG 2, PGH 2 thromboxane A 2 Metabolic pathway of arachidonic acid in platelets

13 Is the vasoconstrictor thromboxane A 2 also made by the vessel wall?

14 Differential bioassay of PGE 2 and vessel wall extract

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16 Arachidonic acid prostacyclin cyclic endoperoxides PGG 2,? thromboxane A PGH 2 2 Metabolic pathway of arachidonic acid in platelets and the vessel wall

17 Aspirin selectively inhibits platelets platelet cyclooxygenase is very sensitive to aspirin* inhibition of platelet cyclooxygenase lasts for the whole lifetime of the platelet *Burch et al (1978) J. Clin. Invest. 61:

18 Arachidonic acid prostacyclin cyclic endoperoxides PGG 2, PGH 2 thromboxane A 2 Effect of low - dose aspirin on the metabolic pathway of arachidonic acid in platelets and the vessel wall

19 Effect of low and high dose aspirin on bleeding time in healthy volunteers Bleeding time (min) Control 0.3 g aspirin 3.9 g aspirin O Grady and Moncada (1978) Lancet 312:780

20 Clinical trials show that aspirin: prevents stroke in patients with atherosclerosis or TIA reduces risk of myocardial infarction in unstable angina reduces mortality in acute myocardial infarction prevents occlusion of vein grafts reduces risk of metastasis in cancer patients

21 Don t use aspirin for primary prevention of cardiovascular disease Barnett et al (2010) Brit. Med. J. 340:

22 It will be difficult to beat old aspirin

23 Cyclooxygenases (1990) COX-1: physiological processes COX-2: inflammatory responses

24 Inhibition of COX-2 results in: inhibition of prostacyclin cardiovascular side effects McAdam et al. (1999) Proc. Natl. Acad. Sci. USA 96:

25 Vioxx settlement to total $4.85bn The maker of Vioxx has agreed to pay $4.85bn to settle legal claims that the controversial drug caused many users to suffer strokes and heart failure. Vioxx was withdrawn from sale in 2004 BBC News Channel, Monday March 12 th 2007

26 Arachidonic acid prostacyclin cyclic endoperoxides PGG 2, PGH 2 thromboxane A 2 Effect of a COX-2 inhibitor on the metabolic pathway of arachidonic acid in platelets and the vessel wall

27 Cardiovascular risk of COX inhibitors Drug Relative risk vs nonuser Naproxen Meloxicam Indomethacin Ibuprofen Diclofenac Rofecoxib (>25 mg) Rofecoxib (<25mg) Celecoxib From: White (2007) Hypertension 49:

28 COX-2 inhibitors may be beneficial in: cancer colon, breast, prostate, lung Alzheimer s disease Parkinson s disease schizophrenia major depression ischaemic brain injury diabetic peripheral nephropathy

29 HOOC O HO OH Prostacyclin

30 Clinical uses of prostacyclin: Primary pulmonary hypertension Peripheral arterial disease Cardiopulmonary bypass Organ transplantation

31 The obligatory role of endothelium in ACh-induced vascular relaxation Furchgott and Zawadzki, Nature 288, , 1980

32 Bioassay of EDRF released from endothelial cells

33 Detection of endogenous and exogenous NO Contracted by U46619 (30nM) A Bioassay Column 1 sec RbA GTN 50nM OT GTN 50nM Bk nm TC NO nmol OT 10 min 2 cm B Chemiluminescence 10 min NO nmol NO Bk nm TC NO nmol nmol Palmer et al (1987) Nature 327:

34 You were very persuasive; but unconvincing! I am sceptical for the simple reason that the formation of nitrogen oxides demands some pretty heavy thermodynamic considerations. Nitric oxide is produced in the upper atmosphere through the energic intervention of lightning!

35 The L-arginine:NO pathway L-citrulline O 2 H 2 N O NH H 2 N NH HO HN NH NH NADPH L-NMMA NH NADPH L-NMMA H 2N COOH NO H 2N COOH L-arginine H 2N COOH N ω -hydroxy-l-arginine

36 Biology of the L-arginine: NO pathway Cardiovascular system Immunology and inflammation L-arginine:NO pathway Nervous system

37 Publications with nitric oxide in the title Cumulative Number of Papers Published

38 The action of nitric oxide In the corpus cavernosum

39 Effect of L-NMMA (100mg kg -1 ) on blood pressure and heart rate L-NMMA 100mg kg -1 L-NMMA 100mg kg -1 L-arginine 300mg kg -1 Rees et al, (1989) Proc. Natl. Acad. Sci. USA 86:

40 The cardiovascular system is in a state of active vasodilatation

41 Nitric oxide inhibits Platelet aggregation Smooth muscle cell proliferation

42 Lack of vascular nitric oxide contributes to hypertension, vasospasm and atherosclerosis

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44 Endothelial dysfunction : predicts disease in patients with a family history of essential hypertension or risk factors for atherosclerosis Taddei et al (1996) Circulation 94: Reddy et al (1994) J. Am. Coll. Cardiol. 23:

45 Oxidative stress: a most significant factor in cardiovascular disease

46 Oxidative stress, prostacyclin and NO arachidonic acid L-arginine PGG 2 prostacyclin synthase 1976 O 2 - X 1986 prostacyclin NO ONOO -

47 Conditions in which ONOO - has been implicated atherosclerosis hyperlipidaemia hypertension myocarditis chronic renal failure septic shock diabetes angiotensin II-mediated vascular disorders cigarette smoking

48 Where do the reactive oxygen species come from? NADPH oxidases xanthine oxidase uncoupled endothelial NO synthase mitochondrial electron transport

49 Formation Nitric oxide of and ROS the in the respiratory presence chain Formation of peroxynitrite of NO NADH succinate I NADH dehydrogenase complex II succinate dehydrogenase complex oo 2 - SOD III cytochrome b-c 1 complex H 2 O ONOO 2 - oo 2 - O 2 IV cytochrome oxidase complex Palacios - Callender et al (2004) Proc. Natl. Acad. Sci. USA 101: NO Cleeter et al (1994) FEBS Letters 345: 50-54